Water heater



FIG. 1 is a front elevational view of the present design;

FIG. 2 is a side elevational view of the present design, the opposite side being a mirror image of that shown;

FIG. 3 is a back elevational view of the present design; and,

FIG. 4 is a top plan view of the present design. 

The ornamental design for a water heater, as shown and described. 